Various analog-to-digital converters are known that convert an analog input to a digital output. Some combination of duty cycle, timing, frequency or a counting of pulses digitally represents the analog input. One known type of analog-to-digital converter circuit is a delta sigma (also called sigma-delta or .SIGMA..DELTA. or .SIGMA..DELTA.) circuit. The delta sigma circuit produces an accurate analog-to-digital conversion, however, it also can produce a repetitive, non-symmetrical digital output that includes harmonic noise at frequencies that can interfere with the converted output. For each analog input level, it is found that tone noise signals at one or more undesired frequencies can appear in the digital output. This tone noise can often fall in the same frequency range as the analog signal, causing interference. In particular, this can be a problem when the delta sigma circuit is used in a vortex flow meter, where the vortex signal itself also tends to be a single tone type of signal. Circuitry in the vortex flow meter, downstream from the delta sigma circuit can lock onto a single noise tone as if it were a vortex signal and give a false reading. There is thus a need to improve the delta sigma circuit to avoid the problems associated with noise tones created in the delta sigma modulator.